In conventional production of metal containers, a large number of manufacturing operations are required to produce common features. Pre-form containers, such as those produced by a drawn-wall ironing process or an impact-extrusion process, typically require a number of forming operations including expanding, necking, flanging, body shaping, embossing, threading, trimming, threading, etc. to produce a finished container. Moreover, each of these forming operations generally requires multiple stages to produce the desired feature. At each stage, a cold-forming or cold-working step is performed by contacting the container with specific tooling such as dies.
Necking a container generally requires between approximately 7 and 17 die-necking stages to produce, depending on properties of the container such as wall thickness and neck geometry. Flanging the container generally requires one or more roll-forming stages. Shaping the body of a container generally requires multiple die-reduction and die-expansion stages, with the number of stages increasing as the complexity of the final geometry increases. Embossing or debossing generally requires one stage of rolling against a tool, or pressure forming into a mold. Threading generally requires at least one roll-forming stage. Trimming generally requires one stage, and multiple trimming operations may be required when multiple necking and shaping stages are performed. For example, one trim may be required after every approximately 8 to 12 reducing or expanding stages. Thus, production of a completely finished container can require 50 or more forming stages.
Conventional machine arrangements for bottle and can manufacturing include a plurality of processing or forming modules extending in a single process line that is typically linear. This is generally referred to as a “machine line.” Containers are passed through the machine line until reaching a desired stage of manufacture. Each module in the machine line receives a container and completes only a single forming stage on the container before passing the container to an adjacent module. Thus, such arrangements generally require a large amount of space in a warehouse, factory, or other location. What is more, each module in the machine line also generally increases operating costs for the system because each module requires individualized maintenance and provides additional points of potential failure.
Another downside of conventional machine arrangements is that each cold-form stage alters the physical properties of the container material, typically making the material more brittle. Thus, the structural integrity of the article is reduced, and additional operations such as heating or lubricating the container may be required to counteract these altered properties.
As an alternative to cold-forming, metal straight-wall pre-form articles or other tubes can be subjected to magnetic pressure, and thereby formed, using a wound-wire electromagnetic coil inserted into the container. When a large electrical pulse is released through the coil, an induced current pulse is produced in the wall of the container. The resulting magnetic pressure can be used to force the wall of the container outward, thereby forming the container. A mold is sometimes used to aid in shaping the container.
These magnetic-pressure systems are generally low-speed, low-throughput, and batch systems. These systems also have significant drawbacks such as inconsistent forming of articles, an inability to produce fine-detail embossing, an inability to produce smooth-sided containers, an inability to produce certain container geometries, or the like. For example, certain container geometries cannot be achieved using electromagnetic systems because the wound-wire coils cannot deliver sufficient electromagnetic force near the lower sidewall of the container due to insufficient clearance between the domed bottom of the can and the sidewall for the electromagnetic coil. One method attempting to cure this deficiency is disclosed in U.S. Pat. No. 5,730,016 entitled “Method and Apparatus for Electromagnetic Forming of Thin Walled Metal.” The system disclosed therein includes an intermediate conductor that is thinner than the coil and, thus, can extend more proximate the domed bottom of the article. The wound-wire coil induces a current into the intermediate conductor, which in turn applies an electromagnetic force on the article. However, this produces a number of drawbacks including a loss of forming power between the coil and the article due to induction of current in the intermediate conductor, a non-uniform force applied in the radial direction due to the required slit(s) in the intermediate conductor, and/or a sizing issue due to the coil and intermediate conductor needing to fit inside of the pre-form article.
Thus, a need exists for systems and methods providing high-speed, high-throughput electromagnetic forming of containers. A further need exists for systems and methods that use electromagnetic energy to consistently form containers having irregular shapes. A yet further need exists for systems and methods that can directly apply electromagnetic forces to low-clearance areas of containers.